I. Field of the Disclosure
The present disclosure relates generally to ejection chips for printers, and more particularly, to a substrate structure for an ejection chip for a printer.
II. Description of the Related Art
A typical ejection chip (heater chip) for a printer, such as an inkjet printer, includes a substrate (silicon wafer) carrying at least one fluid ejection element thereupon; a flow feature layer configured over the substrate; and a nozzle plate configured over the flow feature layer. The flow feature layer includes a plurality of flow features (firing chambers and fluid channels), and the nozzle plate includes a plurality of nozzles.
Narrower ejection chips that are preferred for pagewide ejection devices, i.e., inkjet printheads, require a configuration as depicted in FIGS. 1-3. FIG. 1 depicts a partial perspective view of a conventional narrow ejection chip 100 (hereinafter referred to as “ejection chip 100”) without any flow feature layer and nozzle plate.
The ejection chip 100 is a 1-4 millimeters (mm) wide printhead chip that includes a substrate 110 (silicon wafer), and a plurality of fluid channels, such as a fluid channel 122, a fluid channel 124, a fluid channel 126, and a fluid channel 128, configured within the substrate 110. Further, the ejection chip 100 includes a plurality of fluid ports configured within a top portion 112 of the substrate 110, and coupled with a corresponding fluid channel of the plurality of fluid channels. Specifically, the ejection chip 100 includes a plurality of fluid ports 132 fluidly coupled with the fluid channel 122, a plurality of fluid ports 134 fluidly coupled with the fluid channel 124, a plurality of fluid ports 136 fluidly coupled with the fluid channel 126, and a plurality of fluid ports 138 fluidly coupled with the fluid channel 128. Accordingly, as depicted in FIG. 1, the fluid ports 132, 134, 136, and 138 are provided in the form of arrays at the top portion 112 of the substrate 110 to feed individual firing chambers (not shown) of a nozzle plate layer (not shown) configured over the substrate 110. Specifically, an individual firing chamber is fed by a single fluid port from the fluid ports 132, 134, 136, and 138.
FIG. 2 depicts a simulated view of fluidic path corresponding to the ejection chip 100. The fluidic path is contributed by fluids (inks), such as fluids 142, 144, 146 and 148 that feed respective fluid channels 122, 124, 126, and 128, and the respective fluid ports 132, 134, 136, and 138. Further, the fluid 142 may be a cyan colored fluid, the fluid 144 may be a yellow colored fluid, the fluid 146 may be a magenta colored fluid, and the fluid 148 may be a black colored fluid.
FIG. 3 depicts a bottom perspective (longitudinal) view of the ejection chip 100. Specifically, FIG. 3 depicts a bottom view of fluid paths in the ejection chip 100 with a plurality of ports configured at a bottom portion 114 of the substrate 110 (as depicted in FIG. 1) and fluidly coupled with corresponding fluid channels of the plurality of fluid channels. More specifically, the ejection chip 100 includes a plurality of supply ports 152 fluidly coupled with the fluid channel 122 to carry the fluid 142, a plurality of supply ports 154 fluidly coupled with the fluid channel 124 to carry the fluid 144, a plurality of supply ports 156 fluidly coupled with the fluid channel 126 to carry the fluid 146, and a plurality of supply ports 158 fluidly coupled with the fluid channel 128 to carry the fluid 148. Each port of the supply ports 152 is spaced apart from an adjacent port of the supply ports 152 by a distance of 300-800 microns (μm). Similarly, each port of the supply ports 154, each port of the supply ports 156, and each port of the supply ports 158, is separated by a distance of about 300-800 μm from a respective adjacent port of the supply ports 154, 156, and 158. The spacing among the supply ports 152, 154, 156, and 158 facilitates an easy adhesive dispense to achieve bonding without clogging the supply ports 152, 154, 156, and 158. Further, the each port of the supply ports 152, 154, 156, and 158 is fluidly coupled with a corresponding port of a fluid supply structure/reservoir (not shown) configured underneath the substrate 110, in order to provide a port-to-port connection.
To achieve a narrow structure, such as that of the ejection chip 100, and more particularly, the dimensions of the fluid ports 132, 134, 136, and 138 that are critical for fluid flow resistance to each firing chamber, various methods of fabrication have been employed till date.
FIG. 4 depicts a partial cross-sectional view of a narrow ejection chip 200 (hereinafter referred to as “ejection chip 200”) formed by a conventional fabrication method employing Deep Reactive Ion Etching (DRIE) technique to form a plurality of fluid channels, such as a fluid channel 222 and a fluid channel 224; and to form a plurality of fluid ports, such as a fluid port 232 and a fluid port 234, within a substrate 210 (silicon wafer). Specifically, DRIE technique is used for etching the substrate 210 from a top portion 212 (device side) thereof to form the fluid ports 232 and 234. Further, the fluid ports 232 and 234 may be formed using a control of etching time with an assumption of a fixed etching rate. The fluid ports 232 and 234 may then be filled with a sacrificial material and the substrate 210 may then be ground from backside thereof up to a certain thickness. Thereafter, DRIE technique is used for etching the substrate 210 from a bottom portion 214 thereof to form the fluid channels 222 and 224 fluidly coupled with the fluid ports 232 and 234, respectively.
The ejection chip 200 further includes a flow feature layer 260 configured over the substrate 210. The flow feature layer 260 includes a plurality of flow features (fluid channels and firing chambers), such as a flow feature 262 and a flow feature 264. Each of the flow features 262 and 264 is fluidly coupled to a corresponding port, such as the fluid ports 232 and 234. Accordingly, the fluid ports 232 and 234 are adapted to supply fluids to each respective firing chamber. Furthermore, the ejection chip 200 includes a nozzle plate 270 configured over the flow feature layer 260. The nozzle plate 270 includes a plurality of nozzles, such as a nozzle 272 and a nozzle 274. Each of the nozzles 272 and 274 is fluidly coupled with one or more respective flow features of the plurality of flow features. Specifically, the nozzle 272 is fluidly coupled with the flow feature 262, and the nozzle 274 is fluidly coupled with the flow feature 264.
Similarly, FIG. 5 depicts a partial cross-sectional view of a narrow ejection chip 300 (hereinafter referred to as “ejection chip 300”) formed by another conventional fabrication method that employs undercut etching (chemical etching) technique for etching a top portion 312 of a substrate 310 to form trapezoidal fluid ports (not numbered) as an extension of fluid channels, such as a fluid channel 322 and a fluid channel 324 for reduced flow resistance. Accordingly, the aforementioned method utilizes a single chemical etching process to form the trapezoidal fluid ports.
The ejection chip 300 further includes a flow feature layer 360 configured over the substrate 310. The flow feature layer 360 includes a plurality of flow features (fluid channels and firing chambers), such as a flow feature 362 and a flow feature 364. Each of the flow features 362 and 364 is fluidly coupled to a corresponding port of the trapezoidal fluid ports. Furthermore, the ejection chip 300 includes a nozzle plate 370 configured over the flow feature layer 360. The nozzle plate 370 includes a plurality of nozzles, such as a nozzle 372 and a nozzle 374. Each of the nozzles 372 and 374 is fluidly coupled with one or more respective flow features of the plurality of flow features. Specifically, the nozzle 372 is fluidly coupled with the flow feature 362, and the nozzle 374 is fluidly coupled with the flow feature 364.
However, the aforementioned conventional fabrication methods are incapable of producing uniform and very thin top membrane (less than about 100 μm) at fluid channels. Specifically, the grinding process utilized for grinding a substrate, such as the substrate 210, has a tolerance ranging from about 5 μm to about 10 μm in thickness. Further, DRIE technique and chemical etching technique are associated with an inconsistent etching rate, i.e., there is a certain etching thickness tolerance. Furthermore, fluid channels etched in a substrate may not achieve a high uniformity across either a 6-inch or an 8-inch silicon wafer, due to etching rate non-uniformity caused by plasma density or chemical etchant concentration non-uniformity. Accordingly, top fluid ports in such a substrate have non-uniform thickness across the substrate. The thickness non-uniformity results in flow resistance difference among the fluid ports to firing chambers that leads to quality reduction of inkjet printing. In addition, a DRIE process stopped on a substrate has a curved etching front due to plasma loading effect. Moreover, the need to have sacrificial materials to be filled in fluid ports prior to grinding the substrate from respective backside and etch bottom portion thereof, may lead to inconsistency in the substrate while fabricating an ejection chip.
Accordingly, there persists a need for a substrate structure for an ejection chip and a method of fabricating the substrate structure that provides uniform thickness of a top membrane above fluid channels across the substrate structure while having identical fluidic resistance through fluid ports feeding various firing chambers.